1. Field of the Invention
The present invention relates to a mounting block for a coal bit. The mounting block rotates the coal bit to provide even wear of the bit. The mounting block utilizes Belleville-Type disk springs.
2. Background of the Prior Art
It has been well known to use cutter bits mounted on bit blocks for cutting through coal seams. A source of excessive wear in coal cutter bits has been the inability of the prior art to provide an effective bit rotator. Previously, attempts have been made to provide bit rotation by loosely mounting the bit within the mount and permitting random vibration to rotate the bit. However, this loose mounting permits coal particles to enter the space between the bit and the mount. The coal particles cause the bit to jam so that rotation of the bit ceases. The resulting wear and damage from impact loading results in shortened bit life, increased cutting forces, increased dust generation and increased methane ignition potential. These wear problems are further magnified when automated mining equipment is applied to harder ores. These problems can be expected to escalate as the development of continuous mining equipment for harder ores progresses.
U.S. Pat. No. 3,945,681 was a prior art attempt to provide bit rotation for a coal cutter bit. In this U.S. Patent, three inclined spiral grooves are included in the cutter bit and a follower is provided in the bore. It is intended that the follower will progress from groove to groove as the cutter bit is driven into the bit holder by impact so as to completely rotate the bit. However, this patent fails to provide any sort of positive continuous incremental rotation means. Without such a means of indexing the follower to the next groove, however, the tendency will be for the follower to return to the same groove. U.S. Pat. No. 3,945,681 also includes stop and thrust load surfaces which come into contact and serve as bearing surfaces for the load imposed on the cutter bit. The high friction forces induced between the two surfaces by the large bit loads will prevent the bit from rotating and thus prevent the follower from advancing to the next groove. When this cycle occurs repetitively, a wear pattern will develop which will preclude the follower from ever advancing to the next groove. A further shortcoming of this invention is the proposed use of helical springs. Although the patent shows a relatively compact helical spring used to return the bit to the outward position, in actual practice a helical spring capable of supplying the required return force over the required length of travel simply does not exist since the small helical spring which could fit within the bore of the bit mount could not supply an adequate force to return the cutter bit to the outward position.
It has also been known to use ribs or other appurtenances on the bit body to force rotation of the cutter bit. However, in these expedients the amount of rotation was based upon the depth of the cut so that there was no consistent rotation to promote symmetric wear and increased bit life.